The present invention relates to gas turbine engines and, more particularly, to aircraft-type high bypass ratio turbine engines having multi-stage compressor and turbine sections.
A typical modern gas turbine aircraft engine, particularly of the high bypass ratio type, includes multi-stage high pressure compressor and turbine sections interconnected by a central compressor shaft or, in some models, a forward shaft. In the later instance, the forward shaft extends between the webs of the last stage high pressure compressor disk and the first stage high pressure turbine disk webs. The high pressure turbine section typically includes first and second stage disks, and the compressor section includes a plurality of disks. Located at the radial end of each disk is a row of rotor blades which together rotate around the compressor shaft between fixed stator vanes.
Stator seals are positioned in the combustor section of the engine, one adjacent to the last stage compressor stator and one adjacent to the first stage turbine stator. These high pressure stator seals are an independent component often made of a low coefficient of expansion material or designed to include a closed cavity. These basic stator seal designs produce an adequate frequency margin, between the natural flexural nodal vibration modes of seal components and corresponding seal rotor speed, however these types of designs result in larger than required thermal expansion clearances, since the stator seal and the rotor seal teeth independently react to thermal conditions generated by the engine.
These undesirably large clearances are the result of thermal expansion mismatch of the stator and rotor structure during both transient and steady state operation of the engine. During transient operation, the stator is influenced by relatively high heat transfer values, whereas the rotor bore is surrounded by lower values. These conditions cause the stator to expand significantly faster than the rotor. During steady state operation of the engine, the rotor bore is bathed in temperatures much lower than the stator. This condition drives the stator to expand to, and remain at, a larger diameter which creates steady state clearances larger than desired. Accordingly, there is a need for a stator seal design which minimizes thermal expansion and mismatch at both transient and steady state operation of the engine, and a design which improves performance of the engine with improved thermal expansion clearance control between the rotor seal teeth and the stator seal.